Camshaft bushings are provided for supporting and allowing proper rotation of the camshaft in mechanical brakes for automotive vehicles. Typically, a supporting housing for the bushing assembly is formed from two similar metal plates, each having a generally flat support wall and an outwardly extending protrusion and a converging flange defining an opening through which a camshaft is to extend. The plates are assembled back to back and the oppositely facing protrusions are aligned and their flanges are aligned to form the camshaft opening. An annular bushing having a cylindrical inner surface is positioned in the housing with its cylindrical inner surface aligned with the opening of the housing for receiving the cam shaft. The camshaft bushing assembly is mounted in place on the vehicle by bolting the support walls to the vehicle.
Typically, the housing is manufactured of steel for sturdy, durable use for the lifetime of the vehicle and the internal bushing is made of nylon, plastic or fiberglass filled nylon which is capable of allowing the camshaft which extends through the bushing to oscillate during its braking functions without rapid wear. Nylon and plastic bushings tend to absorb moisture which might cause dimensional changes in the bushing, and these materials have a relatively high coefficient of thermal expansion, which tends to cause structural size changes in the bushing. Such structural changes in the bushing can cause lock-up of the camshaft in the bushing. Fiberglass has been added to nylon bushings to increase the thermal stability of the bushing. However, fiberglass is a more abrasive material, and when it is incorporated in a bushing, it tends to wear out its camshaft, especially if the bushing is not properly lubricated.
Other materials for manufacture of bushings have been taught by the prior art. For example, U.S. Pat. No. 3,589,781 to Hanley et al. teaches a bearing assembly having a bushing made of nylon containing about 30% distributed glass fibers and about 5% molybdenum disulfide. Hanley et al. discloses a bushing that is substantially free of dimensional changes. U.S. Pat. No. 4,036,345 to Webb teaches that a housing for a ball bearing may be made self-lubricating with the addition of graphite or molybdenum disulfide to nylon.
Typically, lubricant, or grease, is provided to the internal surface of the bushing and the facing exterior surface of the camshaft. Lubricant may be provided through a grease fitting port in the housing which communicates with the space between the interior of the housing and the exterior of the bushing, and through holes in the bushing to the facing surface of the camshaft. One prior art bushing has a zerk fitting which threads into a port in the housing. The lubricant applied through the zerk fitting must fill the space between the housing and the bushing before it passes through holes in the bushing to reach the interior surface of the bushing and the facing exterior surface of the camshaft, thus wasting lubricant and not assuring proper delivery of the lubricant to the camshaft. U.S. Pat. No. 3,557,808 to Mathers et al. teaches a brake camshaft bearing wherein a zerk fitting threads directly into a truncated beating ball and delivers lubricant directly to the interior surface of the bearing ball. U.S. Pat. No. 3,819,242 to Robinson also teaches a zerk fitting threaded directly through a bushing.
To better distribute the grease around the inside surface of the bushing and to provide for temporary storage of grease, some bushings have provided longitudinal grooves cut into the inner surface of the bushing. Excess grease may collect in these grooves when the grease is applied through the zerk fitting, and as the camshaft rotates within the bushing the grease will be distributed around the interior surface of the bushing. Typically, O-rings are positioned at opposite ends of the cylindrical bearing surface of the bushing for sealing the area between the O-rings, the cylindrical inner surface of the bushing, and the facing surface of the camshaft against the escape of the lubricant. These O-rings usually are seated in grooves formed between the ends of the bushing and the face or lip of the housing of the bushing. For example, see U.S. Pat. No. 3,589,781 to Hanley et al. and U.K. Patent Application 2,238,834 where the O-rings are located between the lips of the housing and the opposite edges of the bushing.
The manufacturing procedure for producing the camshaft bushing assembly is important. It is preferable that the annular bushing be substantially rotationally immobilized within the housing of the bushing assembly. Movement of the bushing tends to cause excess wear on the bushing and, in a bushing assembly in which the zerk fitting is supported by the annular bushing and not by the housing, as taught by Mathers et al. and Robinson, the zerk fitting may be broken away from the annular bushing by engagement with the metal housing. The manufacturing process should align the longitudinal axis of the bushing with the longitudinal axis of the opening of the housing and should substantially rotationally immobilize the bushing within the housing.
Assembling a camshaft bushing assembly wherein the spherical bushing is supported between two metal plates has been taught previously, as by Mathers et al. by providing an edge of one of the protruding areas of the housing with a recess which permits the spherical bushing to be oriented out of alignment with the opening through the housing, inserted through the recess and into the opening and then the bushing is rotated into alignment with the opening of the housing. The zerk fitting slides into an open edge groove cut in the housing. Having to form a groove and a deflected portion as in Mathers et al., however, tends to render the assembly structurally weak and is undesirable.